The present invention disclosed herein relates to a micro device using micro electro mechanical systems (MEMS), and more particularly, to a condenser-type acoustic sensor.
Acoustic sensors, in other words, microphones convert voices into electric signals. Recently, as it is accelerated to develop small-sized wired or wireless devices, the size of acoustic sensors gradually becomes miniaturized. According thereto, recently, acoustic sensors using MEMS have been developed.
Acoustic sensors are largely classified into a piezo type and condenser type. In case of the piezo-type, a piezo effect, in which a potential difference occurs between both ends of a piezoelectric material when a physical pressure is applied to the piezoelectric material, is used to convert a pressure of a voice signal into an electric signal. The piezo type has a lot of limitations in being applied, due to a low band and uneven characteristics of a voice band frequency. In case of the condenser type, a theory of a condenser, in which two electrodes are opposite to each other, is applied. One electrode of an acoustic sensor is fixed and another functions as a diaphragm. In this case, when a diaphragm vibrates according to a pressure of a voice signal, a capacitance between electrodes is changed and condensed charges are changed, thereby allowing a current to flow. The condenser type has excellent stability and frequency characteristics. Due to frequency characteristics described above, condenser-type acoustic sensors are generally used.